invalid_message_parameters
~~~~~~~~~~~~~~~~~~~~~~~~~~

**type**: ``array`` **default**: ``array()``

When setting the ``invalid_message`` option, you may need to
include some variables in the string. This can be done by adding placeholders
to that option and including the variables in this option::

    $builder->add('some_field', 'some_type', array(
        // ...
        'invalid_message'            => 'You entered an invalid value - it should include %num% letters',
        'invalid_message_parameters' => array('%num%' => 6),
    ));
